#include <iostream>
#include <string>
using namespace std;

class Solution {
public:
    string addStrings(string num1, string num2) {
      int end1=num1.size()-1;
      int end2=num2.size()-1;
      string retstr;
      int next=0;
      while(end1>=0||end2>=0)
      {
        int val1=0;
        int val2=0;
        if(end1>=0)
            val1=num1[end1]-'0';
        if(end2>=0)
            val2=num2[end2]-'0';
        int ret = val1+val2+next;
        if(ret>9)
        {
            next=1;
            ret-=10;
        }
        else
        {
            next=0;
        }
        retstr+=(ret+'0');
        end1--;
        end2--;
      }
      if(next==1)
        retstr+='1';
    reverse(retstr.begin(),retstr.end());
    return retstr;
    }  
};